The electrosyntheses of oxygenated halogen salts of alkali metals and of alkaline peroxide in separate processes and reactors are well known.
For example, conventional chlorate technology is described by J. Coleman in `Electrolytic production of sodium chlorate` A.I.Ch.E. Symposium 204 vol 77 1981. pp 244-263. With minor variations sodium chlorate is produced by electrolysis of aqueous sodium chloride solutions is undivided electrochemical cells. Chlorine is generated at the anode while hydrogen and hydroxyl ions are produced at the cathode of the chlorate cells. The chlorine is hydrolysed to hypochlorite which is converted to chlorate by a homogeneous chemical reaction. The homogeneous reaction to chlorate usually takes place in an external thermochemical reactor. The typical commercial electrosynthesis of sodium chlorate uses saturated solutions of salt at 60 to 80.degree. C. with a chlorine anode operated at current density from 1 to 3 kA/m2. Chromates are usually added to the electrolyte to suppress the loss of efficiency due to cathodic reduction of hypochlorite.
The electrosynthesis of alkaline peroxide solutions by reduction of oxygen in aqueous alkaline solution is described by Berl in U.S. Pat. No. 2,000,815 and by Grangaard in U.S. Pat. No. 3,454,477. Oloman and Watkinson in U.S. Pat. Nos. 3,969,201 and 4,118,305 describe a trickle bed reactor for electroreduction of oxygen to alkaline peroxide and a variation of this method is described by Mcintyre et al in U.S. Pat. No. 4,406,758. This peroxide process is not in commercial use. The process involves the electroreduction of oxygen on a three dimensional graphite cathode in aqueous sodium hydroxide. Typical conditions are a sodium hydroxide concentration from 1 to 3 molar, temperature from 20 to 30.degree. C. and superficial cathode current density from 0.1 to 1 kA/m2. Oxygen gas is delivered to the reactor and superatmospheric oxygen pressure may be used to raise the space time yield of peroxide.
The simultaneous electrosynthesis of two useful products in the same electrochemical cell (one at the anode and one at the cathode) is well known. Hydrogen and oxygen are cogenerated by electrolysis of water in cells where the anode and cathode chambers are separated by a porous diaphragm. Chlorine and sodium hydroxide are cogenerated by electrolysis of sodium chloride in cells divided by cation membranes or porous diaphragms.
The simultaneous electrosynthesis of hydrogen peroxide with other useful products is also described in the prior art. Eng et al in U.S. Pat. No. 3,884,777 show the simultaneous generation of chlorine dioxide, hydrogen peroxide, sodium hydroxide and chlorine in a three compartment electrochemical cell. In this case the peroxide is obtained by anodic oxidation of sulphuric acid.
The simultaneous electrosynthesis of alkaline peroxide and chlorine or sodium chlorate is disclosed by Hideo Yamamoto in Japanese patent 61-284591.(app June 10 1985). Yamamoto describes a divided electrochemical cell with a graphite cathode and noble metal anode. The separator may be a porous diaphragm (which permits the passage of ions and convective flow in both directions) but the examples in the patent use only a cation exchange membrane such as Nafion 315 of duPont. An alkaline peroxide solution is produced in the cathode chamber by the reduction of oxygen in the presence of an organic agent such as a quinone. The organic redox agent can be either dissolved in the cathloyte or coated on the cathode. Chlorine is produced simultaneously at the anode from a solution of sodium chloride. Alternatively, sodium chlorate may be produced in the anode chamber by addition of sodium hydroxide to the anolyte to control its pH around 6.5, to 7.0, in which case Yamamoto must add the complete stoichiometric amount of sodium hydroxide required to neutralize the chlorine generated by the anode. Yamamoto suggests that the sodium hydroxide used to control the pH of the anolyte may be obtained by separating it from the catholyte product by dialysis through an anion exchange membrane but no examples are given for this part of the process. In fact, in his Example 3, Yamamoto adds sodium hydroxide from a separate source.